linux-kernel - [PATCH v2 3/9] mm/huge_memory: support huge zero folio in vmf_insert_folio

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Message-ID: <20250717115212.1825089-4-david@redhat.com>
Date: Thu, 17 Jul 2025 13:52:06 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	xen-devel@...ts.xenproject.org,
	linux-fsdevel@...r.kernel.org,
	nvdimm@...ts.linux.dev,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Juergen Gross <jgross@...e.com>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Matthew Wilcox <willy@...radead.org>,
	Jan Kara <jack@...e.cz>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Zi Yan <ziy@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Nico Pache <npache@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>,
	Barry Song <baohua@...nel.org>,
	Jann Horn <jannh@...gle.com>,
	Pedro Falcato <pfalcato@...e.de>,
	Hugh Dickins <hughd@...gle.com>,
	Oscar Salvador <osalvador@...e.de>,
	Lance Yang <lance.yang@...ux.dev>
Subject: [PATCH v2 3/9] mm/huge_memory: support huge zero folio in vmf_insert_folio_pmd()

Just like we do for vmf_insert_page_mkwrite() -> ... ->
insert_page_into_pte_locked() with the shared zeropage, support the
huge zero folio in vmf_insert_folio_pmd().

When (un)mapping the huge zero folio in page tables, we neither
adjust the refcount nor the mapcount, just like for the shared zeropage.

For now, the huge zero folio is not marked as special yet, although
vm_normal_page_pmd() really wants to treat it as special. We'll change
that next.

Reviewed-by: Oscar Salvador <osalvador@...e.de>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/huge_memory.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 849feacaf8064..db08c37b87077 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1429,9 +1429,11 @@ static vm_fault_t insert_pmd(struct vm_area_struct *vma, unsigned long addr,
 	if (fop.is_folio) {
 		entry = folio_mk_pmd(fop.folio, vma->vm_page_prot);
 
-		folio_get(fop.folio);
-		folio_add_file_rmap_pmd(fop.folio, &fop.folio->page, vma);
-		add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR);
+		if (!is_huge_zero_folio(fop.folio)) {
+			folio_get(fop.folio);
+			folio_add_file_rmap_pmd(fop.folio, &fop.folio->page, vma);
+			add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR);
+		}
 	} else {
 		entry = pmd_mkhuge(pfn_pmd(fop.pfn, prot));
 		entry = pmd_mkspecial(entry);
-- 
2.50.1